The severe thunderstorms occurred along both the surface warm front, which extended from Iowa through northern and eastern Illinois, and a north-south surface dryline which moved into Illinois from Missouri. Preliminary analysis of the WSR-88D data indicates that the storms along the dryline underwent a pattern of cell splitting and merging prior to intensifying into a broken line of tornadic storms that moved across central Illinois.
We are modeling the larger-scale cyclone as well as the severe squall line with the NCAR/Penn. State MM5 mesoscale model. Our research goals in this case include understanding the thunderstorm cell-cell interaction which occurred prior to formation of tornadoes, and the extent to which this evolution was necessary for the development of sustained severe thunderstorms. We will also use the MM5 model solution to generate vertical soundings along the mesoscale boundaries (warm front and dryline). These soundings will be introduced into the COMMAS model, where isolated storm simulations would be performed. The differences between the MM5 and COMMAS simulations should reveal the role of the surface boundaries in the actual thunderstorm evolution.